The invention relates to a device for measuring the spot size of a charged particle beam at wafer level in a charged particle beam lithography system, and a method for manufacturing such a device.
In order to measure the spot size of scanning electron microscope columns, and those used in electron-beam lithography machines, the reflected or transmitted current of a beam is measured as the beam is scanned across a sharp edge, also referred to as ‘knife edge’. Such a method is for example described in J. Phys. E: Sci. Instrum. 17 296, 1984, by S. A. Rishton et. al.
Applying such a method for spot size measurement in a production charged particle beam lithography system, in particular a lithography system having multiple beams, is not straight-forward and poses problems and challenges unknown in research lithography systems:
On the one hand, a production charged particle beam lithography system may use more than 10,000 charged particle beams. In view of this it would be highly desirable to be able to measure a set of charged particle beams simultaneously.
On the other hand, these large number of charged particle beams have a very small spot size and are very tightly packed. The spot size of each charged particle beam can be down to 20 nm or even less, and the pitch between adjacent charged particle beams can be smaller than 100 nm.
It is an object of the present invention to provide a device and a method for spot size measurement at wafer level in a production charged particle beam lithography system.